Arrangement for discharging predetermined amounts of molten metal from a vessel

ABSTRACT

For discharging predetermined quantities of molten metal a gas tight vessel having a discharge conduit is arranged to hold the molten metal. The vessel is connected to a source of a pressurized gaseous medium so that the gaseous medium assists in the discharge of the molten metal. Sensing means are used to generate an output signal, which is representative of the velocity of flow of the molten metal from the vessel, and the signal is passed to an integrating mechanism attains a predetermined value corresponding to the predetermined quantity of molten metal to be discharged, the discharge flow from the vessel is discontinued.

United States Patent Kapun [451 July 11,1972

[54] ARRANGEMENT FOR DISCHARGING PREDETERMINED AMOUNTS OF MOLTEN METALFROM A VESSEL [21] Appl. No.: 874,817

Holz ..266/38 3,363,461 1/1968 Minkoff ...73/ l 98 3,396,870 8/1968Diamond et a1. 164/ 1 55 3,425,483 2/1969 Dearth 164/ 155 3,504,8994/1970 Breuer et al. ..266/38 FORElGN PATENTS OR APPLICATIONS 1,216,5605/1966 Germany ...73/194 EM 1,217,638 5/1966 Gennany ..73/I94EM PrimaryExaminerGerald A. Dost Attorney-McGlew and Toren [5 7] ABSTRACT Fordischarging predetermined quantities of molten metal a gas tight vesselhaving a discharge conduit is arranged to hold the molten metal. Thevessel is connected to a source of a pressurized gaseous medium so thatthe gaseous medium assists in the discharge of the molten metal. Sensingmeans are used to generate an output signal, which is representative ofthe velocity of flow of the molten metal from the vessel, and the signalis passed to an integrating mechanism attains a predetermined valuecorresponding to the predetermined quantity of molten metal to bedischarged, the discharge flow from the vessel is discontinued.

1 Claim, 5 Drawing Figures P'ATENTEDJUL 11 I972 3, 675.911

sum 2 or 2 'FIG.4

INVENTOR BY WHLTEQ KIWW lg-UXM ATTORNEY ARRANGEMENT FOR DISCHARGINGPREDETERMINED AMOUNTS OF MOLTEN METAL FROM A VESSEL SUMMARY OF THEINVENTION This invention is directed to the discharge of predeterminedamounts of molten metal from a vessel, such as a melting furnace, and,more particularly, it is directed to an arrangement for use with closedvessels in which the discharge of molten metal is assisted by apressurized gaseous means, such as compressed air.

In die casting machines or ingot-casting installations, an exact amountof molten metal must be supplied for each casting operation. In the pastthe desired amount of metal has been measured by a ladle which receivesthe metal from a holding furnace. Such an operation is not only verytime-consuming, but the metallurgical conditions requiredto produceuniform castings are affected very adversely because the molten metalcools rapidly as it is ladled from the holding furnace into the mold,for example, an ingot mold, and also because slag and other impuritiesmust be skimmed from the surface of the molten metal bath.

To eliminate these disadvantages it has been attempted to provide anautomatic discharge of the metal from the melting furnace.- However, theapparatus which has been proposed for such automatic discharge has notmet with the desired success.

Means, such as pumps and the like, for handling non-aggressive metalscannot be used for handling the molten metals because of the aggressivecharacter of such metals, particularly aluminum and aluminum alloys andalso because of their high melting temperatures since the meltingtemperatures of the materials used in such means are low.

An apparatus has been disclosed which is especially useful where apressurized gaseous medium is used in assisting in the discharge of themolten metal. In such apparatus the molten metal is contained in anenclosed gas tight furnace vessel in which the surface of the moltenmetal is subjected to a gas pressure and the metal is discharged througha gas tight pipe located near the bottom of the vessel. In thisapparatus the metered amount of molten metal will depend on the gaspressure and the duration of the withdrawal of the metal, provided thatthe level of the molten metal in the furnace vessel remains constant.However, each time the molten metal is discharged from the vessel itslevel drops and the discharge pressure and/or the duration of thedischarge must be varied if equal amounts are to be drawn off from thevessel.

Accordingly, it is necessary to utilize means which sense the level ofthe molten metal in the furnace. Since the furnace atmosphere is hot andthe metal is aggressive, the sensing means used are often damaged andresult in inaccurate readings. Other devices are known for this purpose,which comprise an overflow or valves and similar means for eliminatingthe influence of a varying level in the molten metal.

From the metallurgical viewpoint, it is particularly desirable to use asa furnace vessel a trough-shaped two-chamber induction furnace. In suchfurnaces the amount of discharge will depend on whether the furnace isenergized or deenergized since the electrodynamic pressure influencesthe metered amount discharged. A satisfactory solution to this problemhas not as yet been provided.

In die casting machines, special care is to be taken to avoid any lossof time when the molten metal is being discharged from the meltingfurnace. Since with the means presently available a loss of time cannotbe prevented, the pouring operation will be adversely effected if themolten metal cools too quickly as it is discharged. Further, the moltenmetal may oxidize in contact with the air. The molten metal may becontaminated when it is transferred to a die casting machine through anopen tundish during the pouring operation. To obtain a satisfactorycasting, it is essential that contamination of the molten metal beprevented and that the metal be held at the required pouringtemperature.

The electrodynamic pressure in the melting channel of the furnace maycause the refractory furnace lining to spall off and mix with the moltenmetal. Such a contamination may occur especially in installations inwhich the molten metal is discharged from the furnace by means ofinduction pumps. In other known apparatus relatively delicate orinsubstantial components, such as valves, nozzles and floats, arepermanently in contact with the molten metal or the furnace atmosphere.Still other apparatus are known in which the stroke of a plunger of thedie casting machine is measured as the extent of the discharge material.Such an arrangement has the disadvantage that the flow of the moltenmaterial into the charging chamber results in irregular undulatorymovements on the surface of the molten material so that any measurementsof the level surface are highly inaccurate. It has also been attemptedto use the principle of Heros fountain for metering purposes wherein achange in the pressure of the atmosphere in the furnace chamber causesthe molten metal to be discharge through a duct into a charging chamberor a pouring cylinder of the die casting machine. This apparatus is notcapable of exactly metering the required charge.

Therefore, it is an object of the present invention to measure apredetermined amount of molten metal independently of the level of themetal in the furnace vessel and of any other influences which tend toaffect the measured amount. In accordance with the present invention,this object is attained by means of a device which determines thevelocity of flow of the molten metal and supplies an output signal to anintegrating device which discontinues the discharge flow when theaccumulated signal has reached a predetermined amount corresponding tothe amount of molten metal to be discharged. The velocity of flow of themetal can be measured directly by electromagnetic action in which avoltage, induced by a magnetic field in the molten metal beingdischarged, is measured; or alternatively, in furnaces using apressurized gaseous medium for assisting in the discharge of the moltenmetal, the velocity of flow can be indirectly measured by measuring thevelocity of flow of the pressurized gas.

Where the velocity of the pressurized gas is measured, that portion ofthe velocity of the gas required to increase the pressure in the furnaceto the point at which discharge commences must not be included in themeasurement. Therefore, in accordance with the invention, a switch isprovided which actuates the measuring means when the discharge flow ofmetal begins.

The integrating mechanism consists suitably of a motor having arotational speed that depends on one of current or voltage and arevolution counter which is connected to the motor and initiates thestoppage of the discharge flow of metal after a preset number ofrevolutions has been attained.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,its operating advantages and specific objects attained by its uses,reference should be had to the accompanying drawings and descriptivematter in which there are illustrated preferred embodiments of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a somewhat schematic sectional view of a troughshapedtwo-chamber induction furnace disclosing a particularly suitableembodiment of the present invention in which means are provided forsupplying a pressurized gaseous medium into the fumace for assisting inthe discharge of the molten metal;

FIG. 2 is a diagram representing different curves in which the velocityof the metal being discharged is plotted against time;

FIG. 3 is a somewhat schematic illustration of an electromagneticsensing device for measuring the velocity of flow of molten metalthrough a discharge conduit from a vessel;

FIG. 4 is a view of an integrating mechanism for use in the arrangementdisclosed in FIG. 1; and

FIG. 5 is a view similar to FIG. 1, disclosing another embodiment ofapparatus for measuring the discharge flow of molten metal from avessel.

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1 a trough-shapedtwo-chamber induction furnace is shown and is formed of a furnace vessel1, consisting of sheet steel with a refractory lining 2. The furnacevessel 1 is divided into a charging chamber 3 and a discharge chamber 4interconnected by heating ducts 5. The power for the induction furnaceis supplied by a furnace transformer 6 which heats the metal inductivelywithin the heating ducts because the heating ducts and the adjacentparts of the furnace chamber form a secondary winding cooperating withthe coil of the furnace transformer.

For discharging a molten metal 7 from the furnace vessel 1, assisted bya pressurized gaseous medium, the discharge chamber 4 and the chargingchamber 3 are sealed by means of gas tight covers 8 and 9 respectively.Branch conduits 10, 10 extend from a air conduit 10 and pass through thegas tight covers 8 and 9, respectively, and communicate with thedischarge chamber 4 and the charging chamber 3. A compressor 11 ispositioned at one end of the conduit 10 and an inlet solenoid valve 12is located between the compressor 11 and the branch conduit 10" while anoutlet solenoid valve is located at the opposite end of the conduit 10downstream from the branch conduit 10'. To discharge molten metal fromthe furnace vessel 1, the inlet valve 12 is opened and the outlet valve13 is closed so that the gaseous medium pressurized by the compressor 11is delivered into the charging chamber 3 and discharge chamber 4 forpressurizing the surface of the molten metal 7 and causing it to flowfrom the discharge chamber 4 through a discharge pipe 14 mounted in theupper end of the chamber. As soon as the desired amount of metal hasbeen evacuated through the discharge pipe 14, the inlet valve 12 isclosed and the outlet valve 13 is opened and the pressurization of thesurface of the molten metal is relieved.

T is the time during which the furnace is pressurized (metering time),

F is the outlet cross-section (constant), and

k is the pinch effect factor, the outflowing volume to be metered iswhere v (t) is the discharge velocity as a function of time (FIG. 2).

FIG. 3 shows an arrangement for measuring the velocity of the moltenmetal flowing through the discharge conduit 14. As shown in FIG. 1, thedischarge conduit has a discharge duct 19 which is defined by a pair ofoppositely disposed segments 16 formed of insulating refractorymaterial, such as asbestos cement, and a pair of oppositely disclosedelectrodes 17 formed, for example, of graphite. In other words, as shownin FIG. 3, the discharge duct 19 is rectangular in cross-section and isformed on two opposite sides by the segments 16 and on the other twoopposite sides by the electrodes 17. A permanent magnet or electromagnet18 surrounds the segments 16 and the electrodes 17 and produces a strongmagnetic field about the discharge cross-section of the duct. Whenmolten metal flows through the discharge duct 19, a voltage is generatedbetween the two electrodes 17 and the voltage is proportional to thevelocity of flow of the molten metal.

The voltage generated is applied through an amplifier 20 to anintegrating mechanism 21. The integrating mechanism may consist of anampere-hour meter,which in response to a predetermined preset value,which is the analog of the amount to be metered, operates the controlvalves in the conduit 10 for discontinuing the discharge flow of themetal.

In FIG. 4 a specific embodiment of the integrating mechanism isillustrated and comprises a motor 22, the rotational speed of which isdetermined by one of the current or voltage supplied to the motor.Coupled to the motor shaft is a screw-threaded spindle 23 and a slider24 which is longitudinally movable along the spindle and bears in turnon a slideway 25. When the spindle 23 has performed a number ofrevolutions, the slider is displaced longitudinally and operates one ofa pair of longitudinally spaced limit switches 26 depending on thedirection in which the revolutions of the motor moves the slider 24. Thelimit switch contacted then operates the solenoid valves 12 and 13 forregulating the discharge of the molten metal from the furnace vessel.

Preferably, one of the limit switches is displaceable relative to theother. If the direction of rotation of the motor is reversed after eachdischarge cycle, the distance between the limit switches corresponds tothe predetermined amount of metal to be discharged. Accordingly, a scale27 associated with the displaceable limit switch can be calibrateddirectly to represent the amount of molten metal to be discharged andthe selected amount can be set so that the limit switch defines theextent of the longitudinal movement of the slider for measuring theselected amount of molten metal to be discharged.

In FIG. 5 the arrangement of the furnace vessel 1, with its dischargeconduit 14 and the conduit system 10 for supplying pressurized gaseousmedium into the furnace vessel, is the same as illustrated in FIG. 1with the difference residing in the indirect measurement provided forthe discharge velocity of the molten metal from the furnace vessel.

In the conduit 10 for supplying a gaseous medium into the furnace vessela velocity-sensing device 29 is positioned between the compressor 11 andthe inlet valve 12. The value of the velocity obtained in the device 29is converted in a transducer 30 into an electrical value which passesinto the amplifier 20 and is delivered therefrom into the integratingmechanism 21.

The volume of metal discharged from the furnace vessel depends on thepressure which is generated by the compressor and the volume of air orgaseous medium which is supplied into the vessel.

However, in measuring the velocity of the air or gaseous medium, theamount required to build up the pressure in the furnace until the metalbegins to flow from the outlet opening of the discharge conduit 14 isnot included in the output signal to the integrating mechanism.

To compensate for the pressure build-up required to initiate dischargeflow, a switch 31 is positioned at the outlet from the discharge conduitto initiate the measurement of the velocity of the air or gaseous mediumonce discharge flow has been commenced. This switch consists of a knownnon-contacting proximity switch which is operated as the molten metalstarts to flow from the discharge conduit.

In accordance with the present invention an exact metering of the moltenmetal discharged from a holding or melting furnace is possible withoutinvolving any measurement of the changing level within the vessel or ofany of the other factors which tend to influence the amount of flowdischarged from the vessel. There are no delicate or insubstantial partswhich are permanently in contact with the aggressive molten material orwith the hot furnace atmosphere. Besides, there is no need for meanswhich prevent a formation of additional oxides or which prevent aningress of oxides or other impurities into the pouring device.

Therefore, the arrangement, in accordance with the present invention,may be used in combination with all melting and holding furnaces,particularly for trough-shaped two-chamber induction furnaces using agaseous medium to assist in the discharge of the molten material. In thepast it has not been possible to use automaticallymetered-pressure-assisted discharge with such furnaces.

What is claimed is:

1. A device for discharging a predetermined quantity of molten metalcomprises a vessel for holding the molten metal to be discharged, adischarge conduit connected to said vessel for discharging molten metalfrom said vessel, sensing means arranged to generate an output signalrepresenting the velocity of flow of the molten metal from saiddischarge conduit, an integrating mechanism arranged to receive andintegrate the output signal from said sensing means, control means inoperative communication with said integrating mechanism for interruptingthe discharge of molten metal through said conduit in response to asignal from said integrating mechanism when the cumulative output signaldirected to said integrating mechanism has attained a predeterminedvalue, said integrating mechanism comprises a motor having a motor shaftarranged to rotate at a speed in relationship to the output signalrepresentative of the velocity flow of the molten metal from saidvessel, a variable revolution counter in communication with the motorshaft of said motor for counting the revolutions thereof, said counterin operative communication with said control means for discontinuing thedischarge of molten metal when said counter has counted a predeterminednumber of revolutions, a threaded spindle secured to and extendingaxially from the motor shaft of said motor, a slide member mounted onsaid spindle and movable longitudinally therealong as said spindlerotates, a pair of limit switches disposed in spaced relationship in theaxial direction of said spindle and one of said limit switches beingarranged to be contacted by said slide member at the end of apredetermined number of revolutions by said spindle whereby said controlmeans are operable for interrupting the discharge of molten metalthrough said discharge conduit.

* l i t 1 I UNITED: sqUwriazs 'PATENT OFFICE CERTIFICATE OF CORRECTIONPa'teht 3 75,9 v w t July 11, 197

Inventor WALTER;

QIt i s certified Lthait errora-p pe'ai's the above-identified patentand that said Letters; Patent. are hereby corrected as shown below:

In the heading of the patent, the inventdr's address should read;

- Wurzb'achga sse, Wien, Austria Signed and sealed this 2nd day ofJanuary 1973.

Attesting Officer Commissioner of Patents FORM PO-1050 (10-69) USCOMM-DC6O375-Pfl a [1.5. GOVERNMENY PRINTING OFFICE: 1969 O-366-31

1. A device for discharging a predetermined quantity of molten metalcomprises a vessel for holding the molten metal to be discharged, adischarge conduit connected to said vessel for discharging molten metalfrom said vessel, sensing means arranged to generate an output signalrepresenting the velocity of flow of the molten metal from saiddischarge conduit, an integrating mechanism arranged to receive andintegrate the output signal from said sensing means, control means inoperative communication with said integrating mechanism for interruptingthe discharge of molten metal through said conduit in response to asignal from said integrating mechanism when the cumulative output signaldirected to said integrating mechanism has attained a predeterminedvalue, said integrating mechanism comprises a motor having a motor shaftarranged to rotate at a speed in relationship to the output signalrepresentative of the velocity flow of the molten metal from saidvessel, a variable revolution counter in communication with the motorshaft of said motor for counting the revolutions thereof, said counterin operative communication with said control means for discontinuing thedischarge of molten metal when said counter has counted a predeterminednumber of revolutions, a threaded spindle secured to and extendingaxially from the motor shaft of said motor, a slide member mounted onsaid spindle and movable longitudinally therealong as said spindlerotates, a pair of limit switches disposed in spaced relationship in theaxial direction of said spindle and one of said limit switches beingarranged to be contacted by said slide member at the end of apredetermined number of revolutions by said spindle whereby said controlmeans are operable for interrupting the discharge of molten metalthrough said discharge conduit.